The present invention broadly relates to a new and improved method of, and apparatus for, continuously casting a strand using a curved rigid dummy bar.
In its more specific aspects the invention relates to a new and improved method of, and apparatus for, continuously casting a curved strand using a curved rigid dummy bar, wherein the cast strand is separated from the dummy bar at the region of the straightener or straightening machine by a roller which is movable towards the strand track or path of travel of the strand such that the position of the longitudinal axis of the moving rigid dummy bar is retained.
For the start-up of a continuous casting installation a dummy bar or starting bar is required. The dummy bar head is provided with a coupling member and closes the continuous casting mold at its underside. When the casting operation is started, the dummy bar head produces a connection with the cast strand, so that the cast strand can be withdrawn from the continuous casting mold and introduced into the withdrawal unit.
The dummy bar in curved continuous casting installations may be, for example, composed of individual members or may be constituted by other flexible constructions. Also, the dummy bar may comprise a rigid curved or arcuate piece of steel, generally having the length of approximately a quadrant.
The use of a curved or arcuate rigid dummy bar or starting bar in an arc-type or curved continuous casting installation is known, for example, from U.S. Pat. No. 3,344,844, granted Oct. 3, 1967, wherein the dummy bar is provided with a releasable dummy bar head. The coupling element or member of the dummy bar head comprises an insertable bolt about which liquid steel is cast during the start of the casting operation. The dummy bar head itself is provided with a second coupling element permitting the dummy bar head to be coupled to the dummy bar. At the region of the straightener or straightening machine of this continuous casting installation there is arranged a roller which is movable towards the strand track or path of travel for the cast strand. For separating the cast strand from the dummy bar the movable roller presses upon the cast strand, and thus, disengages the coupling between the dummy bar head and the dummy bar. During such disengagement or decoupling operation the dummy bar moves along its longitudinal axis and remains at its path of movement. The dummy bar head connected to the cast strand passes through shears. The dummy bar head is first separated from the crop end only after the crop-end cut and then is supplied for re-use. Another bolt has to be inserted into the dummy bar head which serves as a coupling element for the next following casting operation or pour.
This state-of-the-art curved continuous casting installation is afflicted with various disadvantages. The dummy bar head remaining at the crop end, which must be manually separated after each casting operation or pour, has to be provided with a new coupling element or member prior to each re-use, has to be recoupled to the dummy bar and has to be protected from or secured against dropping-off. All of these operations or procedures are associated with additional costs. Furthermore, the crop end cannot be faultlessly aligned or straightened in such a casting installation even in the presence of a precise switching pulse for applying the movable press roller at the cast strand, because the strand does not rest upon the straight roller apron or bed during the time of the drive-out or press-out operation. Imprecisely aligned or straightened crop ends at the cast strand, however, frequently cause disturbances when entering a successive shear arrangement.
In a further prior art curved continuous casting installation as known, for example, from U.S. Pat. No. 4,291,748, granted Sept. 29, 1981, a dummy bar contains a rigid portion or member and an articulated flexible portion or member. The rigid member and the flexible member each have a length of approximately half the circular-shaped strand guide or roller apron. The dummy bar head of this dummy bar is provided with a permanent coupling element or member, and the disengagement or decoupling operation is effected by relative movement of the cast strand and the dummy bar head in a direction transverse to the longitudinal axis of the strand. Although approximately only one-half of such a dummy bar is rigid, such construction of dummy bar satisfies two essential requirements for the group of rigid dummy bars. The disengagement or decoupling between the cast strand and the dummy bar is performed at the non-straightened hot strand and the rigid portion or member of the dummy bar bridges larger sections of the secondary cooling zone below the mold and in which sections the strand is not guided. Considering its function, this type of dummy bar which is rigid over half of its length thus can be associated with the group of rigid dummy bars. However, even in such installations the crop end of the cast strand cannot be faultlessly straightened during the time interval of the disengaging or decoupling operation. Depending upon the force required for separating the cast coupling element or member from the dummy bar head the dummy bar may experience a permanent deformation, resulting in difficulties during reinsertion of the dummy bar into the continuous casting mold.